ADCP's Application in Flood Management of Orange River

1. Where is Orange River?

The Orange River is a major river in southern Africa. It originates in the Drakensberg Mountains in Lesotho and flows west by southwest through South Africa.

Geographically, it crosses several types of terrains. In its upper reaches, it cuts through mountainous and high - altitude areas. From here, it flows further downstream through arid and semi-arid regions of the Karoo. It also hosts various cities and towns on its banks, such as Upington in South Africa. The river is a crucial water source for agriculture, with vineyards and other crops in the region depending on its waters for irrigation. It also plays a vital role in the local ecosystem and supports a range of wildlife.

The Orange River Basin has semi-arid conditions in many regions as far as rainfall is considered. The upper parts receive more rainfall, where most of the rain falls as summer thunderstorms and winter snowfall in areas of high elevation. The lower parts have less precipitation, and the river maintains its volume of water inflowing from the upper parts and also from tributaries. However, there are still times when heavy rainfall and floods occur, particularly with the occurrence of an extreme weather event.

2. What are the Causes of Floods in Orange River?

Heavy Rainfall and Snowmelt: Heavy rainfall in the upper catchment area, particularly during the summer months, raises the water volume of the Orange River very fast. During spring, the melting of snow in the mountains sends a deluge of water downstream. These factors put together can raise the inflow into the river beyond its normal carrying capacity and result in flooding.

Tributary Inflows: Orange River has many tributaries that contribute to it. At such instances when the water level is very high in these tributaries either because of heavy rain or other reasons, they contribute a good deal of water to the main channel of the river. If the combined discharge of the tributaries and the main river is greater than what the channel and the floodplains can handle, there will be floods.

Topography and Drainage: These include areas of relatively flat floodplains and some narrow valleys in the course of the river. The flat floodplains can give water a chance to spread out along adjacent areas, slowing down its passage. In the narrow valleys, water level may rise rapidly during periods of heavy inflow. Poor drainage in some areas can also exacerbate the flood situation.

Land Use Changes: Human activities like expansion of agriculture and urbanization have been found to alter the hydrologic cycle. For instance, irrigation development may involve the construction of dams and canals that alters the natural flow of water. Deforestation and conversion of natural grassland into agricultural land decreases the infiltration capacity of the land, increasing surface runoff and, consequently, flooding. In this context, the Acoustic Doppler Current Profiler (ADCP) offers a more advanced and efficient means of measurement for flood - related data compared to traditional methods.

3. How do ADCPs Using the Doppler Principle Work?

The ADCPs work on the principle of the Doppler effect. They emit acoustics into the water. When these acoustic waves hit moving particles in the water-such as sediment, debris, or simply water parcels with different velocities-the frequency of the reflected signals has changed compared to the emitted signals due to the Doppler effect.

The ADCP measures these frequency shifts and, using the known speed of sound in water and the angles of the emitted and received signals, calculates the velocity of the water at different depths. Multiple transducers in the ADCP are arranged to measure velocity components in different directions. By integrating these velocity measurements over different depths and cross-sectional areas of the river, the flow rate and other important hydrological parameters can be determined.

4. What are the Applications of ADCP in Floods of Orange River?

Velocity Measurement: ADCP can effectively measure the velocity of water flow in the Orange River at various points and depths. This is very useful during flood events to understand the dynamics of the flood. It allows for the identification of areas where the flow is rapid and may pose a threat to riverbanks, bridges, and other infrastructure. It further allows the observation of how the flow velocity changes with time as the flood progresses.

Flow Rate Measurement Application: Combining the measured velocity data with the cross-sectional area of the river, ADCP calculates the flow rate. This becomes very important in predicting the amount of water that would pass through any section of the river at the instance of a flood. This would serve in the prediction of the peak flood and its impact further downstream, which is necessary in flood management strategies.

Sediment Transport Studies: Floods in the Orange River carry a great amount of sediment. ADCP is able to study sediment movement through the analysis of acoustic signal echoes that have been affected by sediment particles. This will provide much-needed knowledge about the flood's contribution to evolving the bed of the river through deposition and erosion processes that are key to maintaining stability along the river channel and within the ecosystem.

5. How Can the Data Measured by ADCP Be Utilized for Flood Warning and Risk Management of Orange River?

Flood Warning

Velocity and Flow Rate Data Monitoring: The continuous monitoring of velocity and flow rate data by ADCP facilitates early detection when such parameters are abnormally high. This also forms the basis of detecting any near approach or exceeding critical values of the flow rate, which always precedes flood peaks. In such scenarios, timely flood warnings are therefore sent out to communities and concerned river authorities in good time.

Water Level Prediction and Warning: By correlating the measured flow rate and velocity data with historical water level records, models can be developed to predict future water level changes. This helps in providing advance warnings about potential inundation areas and the height of the floodwaters, allowing people to take preventive measures.

Risk Management

Water Conservancy Project Scheduling Decision Support: The ADCP is able to help make decisions, such as the operation of water conservancy projects like dams and reservoirs along the Orange River. For instance, it is able to help in the determination of the right time and amount of release from the reservoirs to limit the impact of floods downstream.

Assessment of Flood Disaster and Implementation of Emergency Response: When there is a flood, according to the data obtained through the ADCP, the area the flood has covered and the flow characteristics during the period will be estimated. This information leads appropriately to emergency response efforts regarding, for example, the distribution of the relief resources and in plans for post-flood recovery work.

6. What's Required to Obtain High-Quality Measurements of the Currents within Orange River?

For high-quality measurement of Orange River currents, the equipment has to contain material that is reliable. The case needs to be able to bear rough situations such as impacts from floating debris and water with different chemical composition causes corrosion and wide temperature range faced by the semi-arid area.

The size of the equipment has to be small, light, easy to install and deploy in many places on the river, a lightweight that allows it to be transported with fewer resources or cost and installation of the deployed units. It requires low power to be able to perform continuously without high-energy power sources and a battery exchange at too frequent intervals. The system must have low operating costs so it can easily be installed on a large scale and ensure adequate monitoring of the process.

The casing of ADCP is best made of titanium alloy. Titanium alloy enjoys a number of outstanding advantages: It resists corrosion excellently, which is very important in its long-term exposure to the river water. It has a high strength-to-weight ratio, giving sufficient strength while keeping the weight of the equipment at reasonable levels. Its durability ensures stable performance in the different environmental conditions in the Orange River Basin.

7. How to Choose the Right Equipment for Current Measurement?

In the process of choosing the right equipment for current measurement in the Orange River, there are several aspects that one has to consider. If the purpose of usage is solely on horizontal cross - section measurement, then HADCP will be suitable as it measures flow velocity and other parameters across the river section accurately in the horizontal direction. For vertical cross-section measurement, the Vertical ADCP is more appropriate because it can obtain detailed velocity profiles along the vertical axis of the river.

Different frequencies should be chosen based on the actual water depth. For water depths within 70 meters, an ADCP with a frequency of 600 kHz is usually a good option since it can provide relatively accurate measurement results within this depth range. For deeper water areas, up to 110 meters, an ADCP with a frequency of 300 kHz is more suitable because it can penetrate effectively to greater depths and yield reliable data.

There are various ADCP brands available in the market, such as Teledyne RDI, Nortek, and Sontek. However, it is worth highlighting a high - quality and cost - effective Chinese ADCP brand - China Sonar ​PandaADCP. It is made of all - titanium alloy material, ensuring excellent performance and durability. You can find more information on its website: (​https://china-sonar.com/)

Here is a table with some well known ADCP instrument brands and models.